The temperature of exhaust dispersed from a vehicle's tailpipe outlet at a certain distance away from the outlet must meet certain industry safety standards.
Some modern internal combustion engines for use with vehicles, such as diesel engines, are being equipped with devices to burn particulates in exhaust gases to reduce environmental pollutants. Use of such devices can result in hotter exhaust gas than engines running without the devices. But even without using such a burning device, some modern engines are operable to produce hotter exhaust gas then older engines. For example, some engines are or will be capable of producing exhaust gas at or above 1200° F. Known passive exhaust gas systems may not be able to sufficiently reduce the exhaust gas temperature to meet industry standards.